High-density single transistor vertical memory gain cell

ABSTRACT

A memory cell which is formed on a substrate of a first conductivity type. A pillar of the first conductivity type extends vertically upward from the substrate. A source region of a second conductivity type is formed in the substrate extending adjacent to and away from a base of the pillar. A drain region of the second conductivity type is formed in an upper region of the pillar. A gate dielectric and conductor are arranged along a first side of the pillar. A capacitor dielectric and body capacitor plate are arranged along an opposite, second side of the pillar. A depletion region around the source region defines a floating body region within the pillar which forms both a body of an access transistor structure and a plate of a capacitor structure. The cell also provides gain with respect to charge stored within the floating body.

RELATED APPLICATIONS

This application is a divisional application of U.S. patent applicationSer. No. 10/934,299, filed Sep. 2, 2004 now U.S. Pat. No. 7,271,433entitled “High-Density Single Transistor Vertical Memory Gain Cell”which is hereby incorporated by this reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to the field of semiconductor transistors and moreparticularly to a single transistor memory gain cell of high density.

2. Description of the Related Art

Semiconductor memory devices are widely employed in a wide variety ofelectronic devices such as consumer electronics, computer systems, etc.The semiconductor memory devices can provide storage capacity foroperating software as well as data storage, such as for text files,audio/video files, etc. A popular and commonly employed type of memoryis known as dynamic random access memory (DRAM). DRAM provides theadvantage of relatively rapid ability to write and read data as well asa relatively simple circuit design which facilitates relatively highcircuit density and corresponding large memory capacity.

FIG. 1 is a cross-sectional view of a typical prior art DRAM array wherea plurality of individual DRAM cells are arrayed to define a memorycircuit. These prior art DRAM cells are formed in a silicon-on-insulator(SOI) substrate where an active layer of silicon overlies an underlyingburied oxide (BOX) layer. Alternating n-type and p-type regions areformed in the active layer with gate stacks formed to overlie the p-typeregions so as to define an n-type metal oxide semiconductor (NMOS)transistor. The p-type regions are also isolated by the n-type regionsdisposed on either side and the underlying BOX layer to define floatingbodies. As can be seen in the Figure, this defines a generally planarstructure where the various components of the memory cells are alignedin a generally horizontal manner along the major plane of the SOI uponwhich the devices are made.

The usual utilization for the DRAM array is to interconnect the drainregions along a first direction with a bit/data line and the gates alonga second direction via corresponding word lines such that an individualcell can be accessed by addressing the corresponding bit/data line andword line to read from, or write to, the individual cell where thebit/data line and word line intersect. The DRAM cell also typicallyincludes a capacitor structure to which the NMOS transistor isconnected. The capacitor stores charge to define the logic state of theparticular cell. The NMOS transistor acts as an access transistor suchthat by selecting a given access transistor, the charge storage state ofthe associated capacitor can be determined.

There is a continuing desire in the field for increased storage capacityof memory devices, such as DRAM memory, as well as a correspondingdesire for increased speed of operation. This is frequently addressed byreducing the physical size of individual memory cells (scaling), thusallowing a greater circuit density and device count for a given area ofsemiconductor substrate in which the individual devices are formed.However, there are ever-present limitations to the degree to whichfurther reduction in size and corresponding increase in the total countand density of individual devices may be practically realized withcurrent semiconductor processing technologies.

One way of addressing these limitations is to employ innovative devicearchitectures which may facilitate fabricating individual devices ofreduced size. Examples of this can be described with the explanatoryvehicle of a DRAM cell. A typical DRAM cell includes a single n-typemetal oxide semiconductor (NMOS) transistor connected to a separatecharge storage device, such as a capacitor. Thus, scaling to reduce thesize of the DRAM cell involves scaling both the NMOS transistor and thecapacitor charge storage device. Efforts have been made to furtherreduce the footprint, or amount of the planar surface of the substrateoccupied by the DRAM cell, by incorporating vertical structures in theDRAM cell. For example, transistors and capacitor structures are knownwhich extend vertically upwards from the substrate or downwards into thesubstrate, such as with a trench structure. Scaling however can lead todifficulties in operation of the devices as reduction in the size of thecapacitor, as well as reduction in operating voltages reduces theavailable electrical signal output from the memory cells making reliableread/write operations to the memory cells more difficult. An additionaldifficulty is that with the reduced physical size and operating voltagesattendant to scaling, so-called soft errors can more frequently arisewhen incident radiation, such as alpha particles, activates chargecarriers in the cell structure which can lead to errors in the properread/write of the intended logic state of an individual device.

A further difficulty is that trench capacitors formed in the trenches inthe semiconductor substrate are subject to trench-to-trench chargeleakage enabled by the parasitic transistor effect between adjacenttrenches. As the fabrication dimensions are reduced, this leakage effectis enhanced which can drain the capacitor leading to a loss of storeddata. Also, incident alpha particle radiation can generatewhole/electron pairs in the semiconductor substrate which functions asone of the storage plates of the trench capacitors. This can also causecharge stored on the effected capacitor to dissipate, leading to theaforementioned soft errors. Stacked capacitors of a sufficientcapacitance for reliable cell operation present a substantial verticalextent, thus also limiting further reductions in total cell size whilemaintaining reliable cell operation.

It will thus be appreciated that there is a continuing need forinnovative memory cell architectures which can satisfy the continuingdemand for reduced cell size and corresponding increase in device countand density while maintaining reliable device operation and feasible andeconomical fabrication. There is also a need for cell architectures ofreduced dimensions which are resistant to errors, such as the softerrors induced by incident alpha particle radiation.

SUMMARY OF THE INVENTION

Embodiments of the invention provide a high density memory cell.Preferred embodiments avoid the need for expensive epitaxial siliconprocesses and provide a simple device architecture that can be readilyadapted to existing processing technologies. Preferred embodimentsprovide a small footprint and an efficient volumetric use of asemiconductive substrate. Preferred embodiments provide gain withrespect to charge stored in the cell and are resistant to soft errors,such as induced by incident alpha particle radiation.

One embodiment comprises a memory cell comprising a substrate of a firstconductivity type, a pillar of the first conductivity type extendingvertically upward from the substrate, a source region of a secondconductivity type formed in the substrate extending adjacent to and awayfrom a base of the pillar, a drain region of the second conductivitytype formed in an upper region of the pillar, a gate dielectric andconductor arranged along a first side of the pillar, and a capacitordielectric and body capacitor plate arranged along an opposite, secondside of the pillar.

Another embodiment comprises an array of memory cells comprising asubstrate of a first conductivity type, an arrayed plurality of pillarsof the first conductivity type extending vertically upward from thesubstrate, source lines of a second conductivity type formed in thesubstrate extending in a first direction between adjacent pillars andextending substantially adjacent bases of the adjacent pillars, drainregions of the second conductivity type formed in upper regions of thepillar, data/bit lines interconnecting a plurality of correspondingdrain regions and extending in a second direction, gate dielectric andconductors arranged along first sides of the pillars, word linesinterconnecting corresponding gate conductors and extending in the firstdirection, and capacitor dielectric and body capacitor plates arrangedalong opposite, second sides of the pillars.

Yet another embodiment comprises a memory cell comprising a verticallyextending pillar of semiconductor material, a source region formedadjacent a base of the pillar, a drain region formed in an upper regionof the pillar, a gate dielectric and conductor arranged along a firstside of the pillar, and a capacitor dielectric and body capacitor platearranged along an opposite, second side of the pillar wherein chargestored within the pillar determines conductivity between the drain andsource regions so as to define a logic state of the cell.

A further embodiment comprises a method of forming memory cellscomprising patterning and etching a substrate comprised of semiconductormaterial doped a first conductivity type so as to form trenchesextending along intersecting first and second directions so as to definea plurality of vertically extending pillars, filling the trenches withoxide, selectively removing the oxide from trenches extending in thefirst direction, doping upper regions of the pillars and the trenchesextending in the first direction with dopant of a second conductivitytype so as to define drain regions and source lines respectively,depositing gate dielectric along first sides of the pillars, depositingcapacitor dielectric along opposed second sides of the pillars, formingconductive word lines extending along the first direction atop the gatedielectric, forming body capacitor plates atop the capacitor dielectricand forming data/bit lines interconnecting drain regions along thesecond direction.

These and other objects and advantages of the present invention willbecome more fully apparent from the following description taken inconjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a section view of a typical prior art SOI floating body DRAMcells;

FIG. 2 is a section view of one embodiment of high density verticalmemory gain cells;

FIG. 3 is an electrical circuit diagram of the memory gain cells of FIG.2;

FIG. 4 is a circuit diagram of one embodiment of a single memory gaincell;

FIG. 5 is a circuit diagram of another embodiment of a single memorygain cell;

FIG. 6 illustrates parameters for write operations to embodiments ofvertical memory gain cells;

FIG. 7 illustrates parameters for read operations for embodiments ofvertical memory gain cells;

FIG. 8 illustrates one embodiment of a memory gain cell with data or alogic “one” written to the cell;

FIG. 9 illustrates the cell of FIG. 8 in a standby or hold condition;

FIG. 10 illustrates the cell of FIGS. 8 and 9 with a clear or writelogic “zero” condition; and

FIGS. 11 through 15 illustrate intermediate steps of embodiments offabrication of high density vertical memory gain cells.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Reference will now be made to the drawings wherein like referencenumerals refer to like structures and materials throughout. It will beunderstood that the figures are provided for illustrative purposes forthe various embodiments described herein and should not be interpretedas being to scale or illustrating precise quantitative or proportionalrelationships.

FIG. 2 illustrates, in cross-sectional view, one embodiment of a singletransistor memory gain cell 100. The cell 100 provides a readilyfabricatable high-density memory gain cell that can facilitate extremelyhigh device densities and is resistant to soft errors, such as fromincident alpha particle radiation. The structure, operation of, andfabrication of the cell 100 will be described in this embodiment withanalogy to an n-type metal oxide semiconductor (NMOS) transistor forease of understanding. However, it will be understood that in otherembodiments, an analogous complimentary p-type (PMOS) embodiment can beequally realized, as well as a combined n-type and p-type (CMOS)embodiment employing the teachings herein.

In this embodiment, the cell 100 comprises a substrate 102 which, inthis embodiment, comprises silicon p-type doped with boron atapproximately 10¹⁴/cm³. The cell 100 also comprises a generallyvertically extending pillar 104 which, in this embodiment, comprisessilicon more heavily doped p-type than the substrate 102 and in thisembodiment higher than 10¹⁷/cm³. Source lines 106 are also formed at anupper region of the substrate 102 so as to extend generally in a firstdirection 108 substantially along the view of the cross-sectionalillustration of FIG. 2 or substantially into and out of the page. Thesource lines 106 in this embodiment, are positioned adjacent a base ofthe pillars 104 and are further arranged so as to be substantially notunderlying the pillars 104, but rather extending substantially betweenadjacent pillars 104. In this embodiment, the source lines 106 compriseregions of the substrate 102 which have been relatively heavily dopedn-type with phosphorus or arsenic and, in this embodiment, at greaterthan 10¹⁹/cm³.

Drain regions 110 are also formed at upper regions of the pillars 104.The drain regions 110 comprise these upper portions of the pillars 104that, in this embodiment, have been doped n-type with phosphorus orarsenic at greater than 10¹⁹cm³. The drain regions 110 areinterconnected in this embodiment via corresponding data/bit lines 112extending generally in a second direction 113. In certain embodiments,the first 108 and second 113 directions are arranged substantiallyperpendicular to each other, such as for ease of fabrication. However,in other embodiments, the first 108 and second 113 directions intersect,but are not orthogonal.

The source lines 106 define depletion regions 114 and, in thisembodiment, the characteristics of the source lines 106 and dimensionsof the pillars 104 are preferably selected such that adjacent depletionregions 114 merge with each other under the pillars 104. This definesfloating body regions 116 in the pillars 104 comprising p-type materialwhich is isolated or pinched off from the substrate 102 by the depletionregions 114. In this embodiment, lateral dimensions of the pillars 104of approximately 100 nanometers and the source lines 106 formed aspreviously described, will provide these floating bodies 116.

Further in this embodiment, a gate dielectric 120 is formed along afirst side or face of respective pillars 104 and also so as to extend atleast partially over a corresponding source line 106 extending adjacentthe base of the respective pillars 104. In this embodiment, the gatedielectric 120 is formed of 10 nm or less of silicon oxide. Gate/wordlines 122, in this embodiment comprising polysilicon, are formed to alsoextend substantially in the first direction so as to abut acorresponding portion of the gate dielectric along the first face orside of respective pillars 104.

This embodiment of the cell 100 also comprises a capacitor dielectric124 formed along an opposite second face or side of the respectivepillars 104 and along the upper surface of the substrate 102intermediate adjacent pillars 104. In this embodiment, the capacitordielectric 124 preferably comprises a relatively high dielectricconstant insulator and, in this embodiment, comprises aluminum oxideformed with a thickness of approximately 10 nm or less. In otherembodiments, suitable materials for high dielectric constant insulatorscomprising the gate dielectric 120 and/or capacitor dielectric 124include hafnium oxide and zirconium oxide having dielectric constants ofκ≧approximately 25. The cell 100 also comprises body capacitor plates126, in this embodiment, comprising polysilicon extending also generallyin the first direction 108 and formed along the second sides or faces ofthe respective pillars 104.

Thus, in this embodiment, the cell 100 defines a transistor structurecomprising the pillar 104 with p-type floating body 116 region, n-typesource line 106 and drain region 110, gate dielectric 120, and gate/wordline 122. While the cell 100 differs from conventional DRAM cells, thesecomponents do share some similar structural, material, and operationalcharacteristics with conventional planar and vertically arranged NMOStransistors and, thus following reference will be made to an NMOSstructure 130 defined by the substrate 102, the pillar 104, source line106, drain region 110, gate dielectric 120, and gate/word line 122, forease of operational understanding. As previously noted, it will beunderstood that other embodiments comprise a complementary configurationof n-type substrate and pillars and p-type source and drain regionsanalogous to PMOS transistors as well as combined technologies employingboth types.

In this embodiment, a body capacitor 132 is also defined by thesemi-conductive floating body 116 and conductive body capacitor plates126 with the capacitor dielectric 124 interposed therebetween. Thus, thefloating body 116 is comprised both within the NMOS structure 130 aswell as the body capacitor 132. This provides both an extremely highdensity architecture which facilitates advancement in overall cell sizereduction and corresponding increase in device count or density as wellas offering operational advantages which will be described in greaterdetail below. FIG. 3 is an electrical circuit diagram of the embodimentsof the cell 100 previously described with respect to FIG. 2. As can beseen, the floating body 116 is shared both by the body capacitors 132and respective NMOS structures 130.

The operation of various embodiments of single cells 100 will now beexplained with reference to FIGS. 4-10. FIG. 4 illustrates oneembodiment of cell 100 and the operation thereof where, in thisembodiment, the source line 106 is grounded as is the body capacitorplate 126. Operating bias potentials can be applied as shown in FIGS. 6and 8-10. In this embodiment, data or a logic “one” state 134, iswritten onto the cell 100 by applying positive voltage to the gate 122and the drain region 110 which is believed to cause avalanche breakdownand the floating body 116 to collect holes which are generated so as toleave a stored charge 136, as shown schematically in FIG. 8.

A standby, or hold state 140, is realized in this embodiment by placingthe gate or word line 122 at a negative voltage which drives thefloating body 116 to a negative potential by virtue of the capacitivecoupling of the body 116 to the gate or word line 122. This reversebiases pn junctions 156, 160 defined between the floating body 116 andthe drain region 110 and the source line 106 respectively so as toinhibit leakage of stored charge 136 as shown schematically in FIG. 9.

The data, or logic “one” state 134, is cleared by writing a logic “zero”142 to the cell 100 by applying a positive potential to the gate or wordline 122 and biasing the drain 110 to a negative potential, as shown inFIG. 10. This forward biases the pn junction 156 between the floatingbody 116 and drain region 110 and removes the stored charge 136.

Read operations of the cell 100 can be performed by addressing the wordline 122 and determining the conductivity of the cell 100, which in thisembodiment is the conductivity between the drain region 110 and sourceline 106. Thus, in this embodiment, a current I_(DS) 144 between thedrain region 110 and source line 106 of the NMOS structure 130 can beestablished with a potential established therebetween. The I_(DS) 144can be sensed and evaluated in a known manner with respect to an appliedpotential between the gate 122 and source line 106, indicated in FIG. 7as V_(GS) 146. In this embodiment, if the floating body 116 hassufficient stored charge 136 to define a data or logic “one” 134, thebody 116 will have a more positive potential than otherwise. This causesa threshold voltage V_(GS) 146 required to obtain a given I_(DS) 144 tobe lower with data or logic “one” 134 than with logic “zero” 142. Thus,as can be seen in FIG. 7, with a logic state “one” 134 stored in thecell 100, I_(DS) 144 is greater at a given V_(GS) 146 describing a curveI₁ 150. Alternatively, with a logic “zero” 142 stored in the cell 100,I_(DS) 144 is correspondingly lower at a given V_(GS) 146 describing acurve I₀ 152.

Other embodiments will now be described with reference to FIG. 5. Incontrast to the embodiments described with respect to FIG. 4 wherein thesource line 106 and body capacitor plates 126 are grounded, in theseembodiments, either or both of the source line 106 and body capacitorplate 126 are connected to variable voltage sources 154 a and 154 b,respectively. One specific embodiment is to drive not only the gate orword line 122, but also the body capacitor plate 126 to a negativepotential during the standby or hold state 140. In this embodiment, thefloating body 116 is driven to an even more negative potential duringthe standby or hold state 140 to further inhibit the floating body116/drain region 110 pn junction 156 and floating body 116/source line106 pn junction 160 from becoming unintentionally forward biased anddraining stored charge 136.

Another embodiment is to provide a positive potential to the source line106 by the variable voltage source 154 a. This can be used inconjunction with provision of a negative voltage to the word line 122 todrive the pn junction 156 defined by the p-type floating body 116 andn-type drain region 110 as well as the pn junction 160 defined by thep-type body and n-type source line 106 to larger reverse biases duringthe standby or hold state 140. This provides a back-to-back, stronglyreverse biased arrangement between the pn junctions 156 and 160 whichprovides increased resistance against the floating body 116 becomingforward biased during the standby state 140 and thus also increasedresistance to loss of charge 136 due to leakage currents. In oneparticular embodiment, the word line 122, body capacitor plates 126, andsource line 106 are connected with parallel lines and thus all cells 100along a given word line 122 can be simultaneously placed in a givencondition, such as the standby state 140.

A similar alternative embodiment can be provided for the clear or logic“zero” state 142 by driving the word line 122 and/or the body capacitorplate line 126 to a positive potential and the source line 106 to anegative potential. In this embodiment, these lines are parallel andthis will clear, or write logic “zero” 142, to all cells 100 along anygiven word line 122.

The cells 100, in addition to acting as memory cells 100 as previouslydescribed, also function as gain cells 100 by providing a very high gainor amplification with respect to stored charge 136 on the floating body116 of the cells 100. More particularly, a significant change in athreshold voltage V_(GS) 146 is caused by a relatively small charge 136stored on the floating body 116. Correspondingly, a relatively largeincrease (in certain embodiments a factor of approximately one to twoorders of magnitude) in the number of electrons conducted between thedrain region 110 and source line 106 of the cell 100, e.g. I_(DS) 144 isrealized for each stored charge 136.

Thus for example, during a read data operation as previously described,the NMOS structure 130 of the cell 100 can be considered as a transistorproviding gain or amplification. This amplification allows a relativelysmall storage capacitance of the body capacitor 132 comprising thefloating body 116 and body capacitor plate 126 to be effectively usedand avoids the requirements for the capacitance and space requirementsof a relatively large stacked capacitor structure of the prior art.These embodiments thus result in the cell 100 having a very high densitywith an overall area of the cell 100 of approximately 4F² where F is theminimum feature size and wherein the vertical extent of the cell 100 isfar less than the total height of a stacked capacitor or trenchcapacitor and access transistor combinations as are previously known.

An additional advantage of these embodiments is that soft error rates inthe cells 100 are reduced because largely only charge, such as caused byionizing radiation, generated in the relatively small volume of thefloating body 116 in the pillar 104 will be collected. Charge which isgenerated in the substrate 102 by ionizing radiation will be collectedand shorted to ground by the zero biased, or reversed biased, sourcelines 106, depending on the particular embodiment. The retention time ofthe cells 100 will also be longer than known SOI structures since thesurfaces of the floating body 116 comprise high quality oxidized siliconsurfaces with a relatively low surface state generation rate. Thesilicon-insulator interfaces in known SOI structures have, in general, arelatively higher generation rate with corresponding higher leakagecurrents which lead to a correspondingly lower retention time than inthe embodiments described herein.

Further advantages of these embodiments of the cells 100 are that thecapacitance of the body capacitor 132 and, thus, the storage capacitanceof the cell 100, can be readily increased without increasing thephysical size of the cells 100 by using relatively high dielectricconstant insulators for the capacitor dielectric 124 providinginsulation between the body capacitor plates 126 and the pillar 104, andunderneath the body capacitor plates 126. The capacitor dielectric 124is not required to have low surface state densities when deposited onthe substrate 102, in this embodiment comprising silicon, since in thecell 100 of this embodiment, there is no transistor channel which wouldtypically provide a conduction path upward along this surface.Advantageously, a relatively high dielectric constant for the capacitordielectric 124, in this embodiment comprising aluminum oxide, having anegative fixed charge is beneficial by accumulating the surface of thep-type floating body region 116. In other embodiments, the capacitordielectric 124 can comprise other high dielectric constant insulators,such as hafnium oxide and zirconium oxide.

In addition, if the quality of a silicon-insulator interface is good, asin these embodiments, relatively high dielectric constant materials canalso be used for the gate dielectric 120 of the NMOS structure 130 ofthe cell 100 to increase gate drive current. The Applicant haspreviously disclosed a large number of different dielectric materialswhich can be realized, such as by atomic layer deposition, evaporation,and/or the oxidation of metals which can be used for the gate dielectric120 as well as the capacitor dielectric 124. Further information may befound in U.S. application Ser. Nos. 10/739,253 and 10/808,058 both ofwhich are incorporated herein in their entireties by reference.

Embodiments of fabrication of the cells 100 will now be described withreference to the illustrations of FIGS. 11-15. As shown in FIG. 11, thesubstrate, or wafer 102, is first oxidized to provide an oxide layer 202approximately 10 nm thick. Then a silicon nitride layer 204 is depositedto act as an etch mask. The silicon nitride mask layer 204 andunderlying oxide 202 are patterned and then an anisotropic etch 206 isperformed to create intersecting trenches 210 extending in the firstdirection 108 and trenches 212 extending in the second direction 113 asshown in FIG. 12.

The trenches 210, 212 are then filled with oxide 214 and the wholestructure is planarized, in this embodiment by chemical mechanicalpolishing (CMP). The oxide 214 is then removed from the trenches 210such that oxide 214 remains in regions of the trenches 212 notcoincident with the trenches 210 as shown in FIG. 12. Thus, oxide 214 isinterposed between adjacent pillars 104 along the first direction 108,but substantially absent along the trenches 210.

The source lines 106 are formed in the trenches 210 with the parameterspreviously described as illustrated in FIG. 13. The drain regions 110are also formed in the upper regions of the pillars 104, also aspreviously described. The placement of the source lines 106 along thelower edges of the trenches 210 provides a simplified manufacturingprocess as, in one embodiment, a single implantation step can beperformed to provide the n-type doping previously described so as toform both the source lines 106, positioned along the bottom of thetrenches 210, as well as the drain regions 110 atop the pillars 104 in asingle implantation step.

The gate dielectric 120 and capacitor dielectric 124 are formed asillustrated in FIG. 14. In this embodiment, the gate dielectric 120 andcapacitor dielectric 124 are formed together. The gate/word lines 122and body capacitor plates 126 are then formed as shown in FIG. 15. Thedata/bit lines 112 can also be realized by conventional metallurgytechniques. General techniques and processes adaptable for forming theembodiments of cells 100 described herein can be found in U.S. Pat. Nos.5,936,274; 5,973,356; 5,991,225; 6,072,209; 6,097,065; 6,124,729;6,143,636; 6,150,687, 6,153,468; and 6,238,976 which are allincorporated herein in their entireties by reference.

Thus, an array 216 of the cells 100 is provided. In this embodiment,individual cells 100 comprising the pillars 104 are positioned in thearray 216 in a generally uniform rectangular arrangement defined by theintersecting trenches 210 and 212 extending generally along the firstdirection 108 and second direction 113, respectively. It will beappreciated, however, that in other embodiments, the arrangement ofindividual cells 100 in the array 216 can adopt an offset substantiallyrectangular arrangement or non-rectangular arrangement withoutdetracting from the scope of the invention.

The embodiments of cells 100 previously described also provide aparticularly efficient volumetric usage of material as a single regionof material, the floating body 116, comprises both a body of the NMOSstructure 130 as well as the body capacitor 132. This provides both aparticularly efficient use of the material comprising the cells 100, aswell as providing reduced exposure for soft error occurrences, aspreviously described.

The cells 100 admit use of relatively high dielectric constantinsulators as well as provide both memory and gain functionality. Thecells 100 are much simpler than conventional stacked capacitor or trenchcapacitor DRAM cells and have a shorter vertical extend. The cells 100replace the relatively large storage capacitors which consume asignificant footprint in known DRAM cells with the relatively muchsmaller body capacitor 132. These cells 100 further utilize the activegain of the NMOS structure 130 to amplify any stored charge 136.Specialized processes are not required for the fabrication of the cells100 and, thus, can be implemented using standard CMOS processingtechniques providing significant financial advantages for implementationof the embodiments described herein.

Although the preferred embodiments of the present invention have shown,described and pointed out the fundamental novel features of theinvention as applied to those embodiments, it will be understood thatvarious omissions, substitutions and changes in the form of the detailof the device illustrated may be made by those skilled in the artwithout departing from the spirit of the present invention.Consequently, the scope of the invention should not be limited to theforegoing description but is to be defined by the appended claims.

1. A method of forming memory cells comprising: patterning and etching asubstrate comprised of semiconductor material doped a first conductivitytype so as to form trenches extending along intersecting first andsecond directions so as to define a plurality of vertically extendingpillars; filling the trenches with oxide; selectively removing the oxidefrom trenches extending in the first direction; doping upper regions ofthe pillars and the trenches extending in the first direction withdopant of a second conductivity type so as to define drain regions andsource lines respectively; depositing gate dielectric along first sidesof the pillars; depositing capacitor dielectric along opposed secondsides of the pillars; forming conductive word lines extending along thefirst direction atop the gate dielectric; forming body capacitor platesatop the capacitor dielectric; and forming data/bit linesinterconnecting drain regions along the second direction.
 2. The methodof claim 1, wherein patterning and etching the substrate comprisesforming an oxide layer and then a nitride layer and patterning the oxideand nitride layers so as to define an etch mask and performing ananisotropic etch through the mask.
 3. The method of claim 1, wherein atleast one of depositing gate dielectric along first sides of the pillarsand depositing capacitor dielectric along opposed second sides of thepillars comprises depositing a high dielectric constant material havinga dielectric constant of κ≧25.
 4. The method of claim 3, wherein thehigh dielectric constant material comprises aluminum oxide.
 5. Themethod of claim 1, comprising forming the trenches such that the firstand second directions are substantially perpendicular to each other.